Introduction:
Gun Bros is a twin-stick, top-down, freemium shooter from Glu Mobile. You are part of a brotherhood tasked with defending the universe from an evil force. The game itself it free and you only need to spend your real-world cash if you want to skip some grinding and pace faster through the game. This is an entirely single-player experience. However, because of the way the game is set-up, it feels like much more than that. You can recruit your friends characters to fight at your side and even complete challenges with your friends. You also earn extra bonuses when your friends play with your character in their game. This guide is based on the premise that you do not spend any money at all on the game. If you break down and pay the outrageous prices for war bucks, you could possibly complete this a little faster. The game is currently listed as FREE on the Marketplace.

*NOTE*: As more and more days pass since the game's release, new glitches are being uncovered. They range from annoying to game breaking. Many of them could drastically lengthen your path towards the 200 or possibly even make it unattainable. A full list of glitches can be found in THIS thread. The worst of them all? Your entire progress through the game being lost. Considering the shear number of glitches and the amount of people reporting them, it may be best to wait for a patch before attempting this game. Glu's other freemium title, Bug Village, was similarly glitched at launch, but was patched shortly after its release. Gun Bros will likely see the same treatment.

Step 1: Hook yourself up with 10 bros:
In short, adding folks to your friends list who also have this game will make completing this game faster because you are granted several bonuses, called Bro Buffs, which boost your stats, as well as the coins and experience your earn. Your first step should be searching for and adding other people to your friends list who have this game. See "Buffed-Up" for a link to a thread.

Step 2: Complete all 10 Revolutions on a single planet:
You should begin by choosing a planet and begin completing the Revolutions. Completing the 10th Revolution on a single planet involves beating 500 waves of enemies and will earn you the "Omega" achievement. You will most likely be able to attain all other achievements, except "Legend," alongside completing the "Revolutions."

Step 3: Grind to Level 100 for the "Legend" Achievement:
Depending on your play style, you will likely have to grind some levels after completing 10 Revolutions. The good news is, however, that there are some good places to quickly rack up some XP. See "Legend" description.

Conclusion:
All in all, Gun Bros is a well-designed freemium game. Unfortunately, once the initial buzz from the great design and gameplay mechanics wears off, it becomes nothing more than a long, long grind to get the full 200 gamerscore. While it is enticing to purchase in-game currency with real-world cash to reduce the grind-time, the costs by most will be considered just too high. 135 gamerscore can likely be obtained in a modest 10 hours or so (not getting "Omega," "Annihilator," or "Legend"). If you are looking for the full 200, expect to put significant amounts of time into this game.

These three achievements just require you to get a certain amount of kills. All types of enemies and all planets count, even if you fail a wave. These will come with natural progression towards reaching Level 100. However, if you want to get this out of the way and "boost" it, playing Survival on the third world Bokor is your best bet. Use the Corona Ejector in the Bokor camping spot found in this video. Your kills per minute will range from 500-1000.

These achievements require you to level your character to 20, 50, and 100. Leveling is achieved by XP which is gained from killing enemies. You should also keep as eye out for XP pick-ups which are occasionally dropped by more powerful enemies. These provide boosts to your XP. This will most likely be the last achievement you unlock as all others should be easily attainable on route to this one.

The fastest way to boost levels in this game is to play against hordes of Zombies on Bokor, whether you are racing for 100 or just need a little extra boost to beat a Revolution. The video below, found by VV1pCr3am, shows a great spot to camp with the Corona Ejector, at the 3:15 mark of the video added to the "Annihilator" achievement.

To unlock these achievements, you must complete all then Revolutions on one planet. A Revolution consists of 50 waves of enemies, meaning in total you must complete 500 waves of enemies to unlock Omega (50x10). Each Revolution's enemies are stronger than the last's. Just keep leveling your character and buying better guns and armor. It also does help if you can recruit a friend that has a similar level as you or even higher. In that case, you can tear through the levels without dying too much. If you find you have the best guns and armor, you may need to grind a few levels (which increases your overall health) and try again. The ladder Waves of each Revolution do become a bit challenge. When you get surrounded by too many enemies, use a Green Shield power-up (makes you invincible for a short time) to plow through one direction and escape unharmed.

The video below shows grind spots for each planet, credit to VV1pcr3am for find this video. These types of spots allow you to control the spawn of the enemies and survive longer.

NOTE: Once you complete Wave 49 of Revolution X, you will be booted out of the game and be congratulated for completing the Revolution. However, to actually earn the achievement, you need to go back in and actually complete Wave 50.

Purchase 20 different pieces of armor from the store. This could be hats/helmets, armor, or pants. The cost of the 20 cheapest armor pieces combined is approximately 10,000 coins. In general helmets are cheapest.

You need to get perfect on 100 different waves. To get perfect, you must complete the entire level without taking any damage at all. This will come with time. The first 20 levels of each revolution on each planet are quite easy to get perfect on as there are not that many enemies and they are generally week. If you want to get this out of the way, just replay any waves early in the revolutions on all planets (first 20 or so) until this unlocks. Remember, it must be 100 UNIQUE waves...you cannot keep playing the same wave over and over getting perfect to unlock this. It will only count as one.

These achievements are require killing 1,000 enemies of any type in any mode with the specified type of gun. There are four main types of guns in the game: pistols, rifles, shotguns, and spread guns. There is one achievement for each. You can see a weapons type before you purchase it in the bottom left of the weapons box in the store. These can be obtained in normal progression, but I myself really only like to use spread guns/Corona Ejector. In this case, they can easily be boosted against the zombies on Bokor in Survival. Use the camping spot mentioned in the "Annihilator" achievement.

Killing enemies and completing waves earns you Xplodium, which after you die and return to the menu can be placed in refineries and converted to coins. Here is where the time element comes into this game. You can refine your Xplodium instantly but earn less coins, or you can put it in specified refineries that take longer (10min, 30min, 24hrs, 72hrs) to get more coin in the end for your wait. If you have the best armor and weapons in the game already, besides power-ups, there is not much to spend cash on. This should come with natural progression. If you tear through a ton of waves without dying, it would be a good idea to deposit that large amount of Xplodium into the 72-hour refinery as you get a 400% coin (more if you have Bro Buffs) return, but you do have to wait three days. Do not worry about this too much, as by the time you get to Level 100, you will have upwards of 1,000,000 coins or more in the bank.

This achievement can only be earned on the planet Bokor against the zombie horde. You need to get your streak up to 30 kills. Your streak stays active as long as you do not take any damage. Getting 30 is ridiculously easy and you will definitely get this without even trying. The counter for your streak is the large number displayed in the top right corner of the screen in red.

*REQUIRES INTERNET CONNECTION* Bro-Ops Challenges change daily and can be found under the "Bro-Up" tab from the main menu. There are four each day, and the top ones tend to be much easier than the bottom ones (and hence offer much lamer rewards). To unlock the achievement, all you have to do is complete the task unlocking the first reward. If your Bros also complete the challenge, you can unlock more rewards.

*THIS MAY REQUIRE AN INTERNET CONNECTION* Bro Buffs are just the boosts you get from having "bros," or friends, that play the game. The more bros you have, the better the boosts you get. It is advised that you acquire the allowed maximum of 10 bros in order to decrease the overall completion time, as almost every aspect of the game is boosted when you have bros. See this forum if you need more bros.

**GLITCH** Some folks are having trouble getting their friends with the game to actually show-up as bros, making this achievement unattainable. The problem seems to be specific to certain countries (Norway, Nederlands...), but may be a small issue everywhere. It could possible be related to individual phone models, but that does seem unlikely as it has been reported on the Titan and Lumia 800. "The Bro-Up" achievement is still obtainable however.